A respirator with a compressed gas reservoir and a warning device, which sends an acoustic signal in the form of a whistling sound when a warning pressure is reached, has become known from DE-AS 11 29 376. A lung-controlled valve located on a breathing mask is connected to two compressed gas sources via a connection piece. One of the compressed gas sources is fastened on the back of the user of the apparatus. The other compressed gas source is arranged stationarily away from the user of the apparatus, and the compressed gas is fed to the lung-controlled valve via a flexible supply tube. In the normal case, the user of the apparatus receives his breathing gas via the flexible supply tube from the stationary compressed gas source. When the supply pressure drops below a certain value, a changeover is performed by means of a pressure-actuated changeover switch to the compressed gas cylinder located at the user of the apparatus, and a partial flow, which reaches an acoustic signal device, is branched off at the same time from the gas flow sent to the lung-controlled valve.
The drawback of the prior-art device is that the acoustic signal is felt by the user of the apparatus to be disturbing, and the gas flow flowing through the signal device additionally consumes some of the gas present in the breathing gas reservoir. In addition, an acoustic signal is not always perceptible in case of louder ambient noise.
Warning devices in which the inspiration resistance is increased have been known as well. Their drawback is that the user of the apparatus does not receive a sufficient amount of air any longer and may panic.
Electronic warning devices require a considerable design effort due to the compliance with the explosion protection regulations.